WPW | Notion

Wolff-Parkinson White

Wolff-Parkinson White (WPW) syndrome is Most common type of ventricular preexcitation syndrome caused by a congenital accessory conducting pathway between the atria and ventricles leading to atrioventricular re-entry tachycardia (AVRT). As the accessory pathway does not slow conduction AF can degenerate rapidly to VF.

Image sourced from Wikipedia

Orthodromic AVRT (most common, ~90%)

Feature	Description
Direction of impulse	Down the AV node → Up the accessory pathway
QRS width	Narrow (normal ventricular activation via His–Purkinje)
Mechanism	The impulse travels antegrade through the AV node, activates ventricles normally, then re‑enters the atria retrogradely via the accessory pathway
ECG features	- Regular narrow‑complex tachycardia

P waves often seen just after QRS (retrograde atrial activation)
No delta wave during tachycardia | | Treatment | Same as other SVTs — vagal manoeuvres, adenosine, or AV nodal blockers (if no pre‑excitation on baseline ECG) |

Antidromic AVRT (rare, ~10%)

Feature	Description
Direction of impulse	Down the accessory pathway → Up the AV node
QRS width	Broad (ventricles activated abnormally via accessory pathway)
Mechanism	The impulse bypasses the AV node antegradely, depolarising ventricles directly, then re‑enters atria retrogradely through the AV node
ECG features	- Wide‑complex tachycardia (can mimic VT)

Delta‑like slurred upstroke
Retrograde P waves may be hidden | | Treatment caution | Avoid AV nodal blockers (adenosine, verapamil, digoxin, β‑blockers) — they can worsen conduction down the accessory pathway and precipitate VF. Use procainamide or DC cardioversion instead. |

<aside> 💡

Orthodromic: “Normal route down, shortcut up.” → Narrow QRS
Antidromic: “Shortcut down, normal route up.” → Broad QRS </aside>

Possible ECG features include:

short PR interval
wide QRS complexes with a slurred upstroke - 'delta wave'
left axis deviation if right-sided accessory pathway
- in the majority of cases, or in a question without qualification, Wolff-Parkinson-White syndrome is associated with left axis deviation
right axis deviation if left-sided accessory pathway